Morphologi cTransformatio no fth eThymu si nDeveloping Zebrafish

Th emorphologi ctransformation o fth edevelopin gzebrafis hthymu sfro m 1week postfertilizatio n(wpf )t o1 5wp fi sdescribed .The thymu soveral lmorpholog ychange dfro ma small pouch-lik eshap ea t 1wp ft oa conica lshap ebe- twee n 2an d3 wp fbefor eacquirin ga mor ecom- ple xshap efro m 4wp fonward .Rapi dgrowt hrate alon gth elatera laxi sa tth eregio nnea rth epha- ryngea lepitheliu moccurre dbetwee n1 an d2 wpf, wherea srapi dgrowt hrat ealon gth edorsal-ven- tra laxi soccurre dbetwee n3 an d6 wpf .Expansion o fthymocyt epopulatio nbeginnin gfro m 1wp fbe- cam emor eeviden tb y2 t o 3wpf ,a sindicate dby th eapparen tincreas eo fdifferen tsize so flympho- cytes ,recombinatio nactivatin ggene- 1(rag-1) ,and T-cel lantige nrecepto ralph achai nconstan tre- gio n(TCRAC )-positiv ecells .Tissu esectio ni nsitu hybridizatio n(ISH )analysi swit hrag- 1prob ere- veal stha tcortex-medullar yregionalizatio nha sbe- gu nbetwee n 1an d2 wp fa srag- 1expression clearl ydemarcate dth ecortex ,wherea sth eme- dull awa srag- 1negative .Th epresenc eo fTCRAC- positiv ecell si nth emedull ab y2- 3wpf ,suggests tha tth ethymi cselectio nprocesse sha dbegun .The zebrafis hthymu si smorphologicall ymatur eby 3wpf .Earl ysign so fthymi cinvolutio nwer eob- serve di nzebrafis hage d1 5wpf. ©200 2Wiley-Liss ,Inc. Ke ywords :zebrafis hdevelopment ;thymus ;mor- phologi ctransformation ;cortex-med- ullar yregionalization ;recombination activatin ggene-1 ;T-cel lreceptor